I am building a new listening room, in a small space. looking at bass trap options, i have the ability to raise the floor to about any height i wish. I was wondering if it is a possibility to make the floor into a large bass trap? I originally planned to raise the floor 6" from the concrete, install insulation between the floor supports, and cover with plywood and then hardwood flooring over that. the the 6" air space and the insulation below the floor serve as a bass trap? or will the plywood and hardwood flooring be too thick for the low freqs to pass?thanks for any input.

i hope so too...id really like to know. for that matter, the celing should be a hell of a bass trap too...unless there is something i grossly misunderstand. it seems the "low" frequencies pass through the surface objects, and into the insulation layer, but dont travel back out. i dont quite understand how that works.also, am i to understand, that if a given bass trap is engineered to trap freqs down to say, 40hz...then it will also trap frequencies above that range? at least in the bass region (say 40-120)...just for argument.thanks for looking.on a side note, the ceiling comment, i have a ranch style home with a drywall celing and blown insulation about a foot thick above, into an empty attic space. i have read steve's notes on room treatment, and many others as well. just a few things i dont quite understand the science of.

However, simply filling it with 6 inches of insulation would be a total waste compared to what is possible.

In the area that I installed a similar floor over concrete I did just that, but the room in question didn't need any more bass traps. I did it so I would have a floating floor that collected and transferred energy through the listening chair to the listener. It added tremendous life to music vs. sitting on the concrete. It also had some nice trapping effects down to probably 150/200 Hz at best.

If you want a real bass trap, you'll want to create a diaphragmatic absorber under the floor in place of the insulation. You will use 3/4 plywood on 2x6 or 2x8 or 2x10 or 2 x 12 inch joists. The cavity that the joists create must be air tight. Joists must be glued to the floor and air tight. Install two layers of large size bubble wrap on the concrete to create effectively a 1 inch air space. Then lay down a layer of 2 inch thermafiber aka rockwool OR Ownens Corning's high density 2 x 4 panels of 701 (I think it's 701 or 702). Then install another layer of bubble wrap to create the second 1 inch air space and add ANOTHER layer of the 701 or 702. Repeat this layering process, (1 inch air space + 2 inch high density fiberglass) until you have reached the top of your floor joists. This would be a serious bass trap. 12 inches gives you linear absorption down to 60 Hz.

If you can do anything you want, perhaps create a 6 inch depth floor and wrap the outside edges of the room with a 12 inch floor- effectively creating a sunken living room. The outside part that is 12 inches deep would trap low frequencies, while the 6 inch depth floor would trap higher frequencies.

Just remember, a bass trap (a real one anyway) consists of a sealed box with no air leaks and no internal bracing filled with alternating layers of high density fiberglass and dead air spaces. It can be any shape you wish. The depth of the alternating layers determines how low it will absorb. To get down to 20~30Hz range you need about 18 inches of depth. 12 inches usually hits around 60 Hz. In comparison, a piece of regular house fiberglass insulation, or foam tiles would need to be some 15 foot thick to absorb bass in the 20~30 Hz range and it is proportional.

The reason the alternating layers of dead air and high density fiberglass works in less than 1/4 the depth is because of the layering aka diaphragmatic action of each layer. As each layer resonates independently of the other, it converts the sound energy into heat and the heat, unlike the sound energy, does not come back out of the box. The heat is caused from friction. The friction is caused from air molecules colliding with each other and with the high density fiberglass. Air molecules that are moving at the speed of sound are de-accelerated by the fiberglass particles. The air space between each layer creates impedances in the resonance that shift in phase backward in time with each consecutive layer. The contrasting phase angles meet in the dead air space between each layer causing some cancelation of the sound. This is why the layering effect is 4 times more efficient than the same depth of a single layer.

Before you begin you room, buy the book "Masters Handbook of Acoustics" by Everets. It's an easy read, has the minimal math required to calculate absorbtion, diffusion and gives several examples of extreme listening rooms, which is another term for Recording studios. It will give you the knowledge you need to be HIGHLY effective with your money.

Example, one man has a box of 2 inch foam tiles and he puts them on the walls of his listening room where he thinks they might be effective. Another man reads the handbook and places the same number of tiles in the exact locations where they WILL be most effective and actually hears a profound improvement while the first is still in the "I think I can here it zone"

Knowing where to place acoustic treatments is at least 400% more important than how many you purchase. The shits not cheap, you could by 4 or 5 times more treatment than you need because you didn't put it in the exact right spot. The book is around 30 dollars. You will know exactly where and what to do, how to do it, how to build it.

You'll also get enough of a basic understanding of all this to distinguish BS from the real thing. You'll be able to do the math and see that it takes 20 tube traps to equal one 150 lb diaphragmatic absorber. You discover that diaphragmatic techniques render linear results - meaning equal absorption at all frequencies within it's design band... Usually several octaves.

BEFORE I bothered to read this book, I took a perfectly good space and build a hideous sounding listening room. It had concrete floors. I put indoor outdoor carpet on the floor that was glued down to the concrete. At that stage I put my favorite speakers in the room and they had no bass, not to mention sounded like crap.

I ended up having to cover 2 walls floor to ceiling corner to corner with 2 inch foam tiles before it sounded just OK. I had bass now. Because the 2 inch tiles acted as bass traps... NO. Because the 2 inch tiles absorbed mid and high frequencies from 1K on up. See, the bass was always there... the highs were just 12 dB too loud.

Now the room looks stupid. I find out after reading the book, that had I installed a thick pad under the carpet and used a thicker carpet to begin with, I would have had the same number of Sabins of absorption as the two walls covered with foam. So I got new carpet and put a pad under it, removed 100 percent of the foam tiles on the walls and had the exact same frequency balance. The tiles cost 2.00 each. I used 306 of them, and then removed 306 of them.

I also learned about golden ratios and how they effect standing wave patterns in the room. I then raised my ceiling 3 inches, moved one wall in 10 inches and the other out 4 inches to hit that ratio. Now there are greatly reduced holes in the bass as you walk through the room.

Can you see how much money I could have saved, not to mention time, had I read the book before I started...

Many years of practicing the information in that book has confirmed it is accurate.

Low frequencies can easily pass through solid concrete several feet thick. To a bass note, a 3/4 inch thick board appears only as a minor nuisance, Not unlike a bullet going through toilet paper.

I have seen with my own eyes a low frequency bass wave pass through a concrete block wall without moving even a grain of dust on that wall while at the same time blowing a 14 foot diameter hole through the concrete wall on the other side of the building. Sound is incredibly fascinating, powerful and elusive - due to other sound, or put another way, the sound that follows it. A single wave front (pulse) by itself is powerless by comparison to that same pulse relative to successive wave fronts and the timing between them. AKA phase angle vs frequency. This is how is was possible to calculate a frequency that would pass through 1 concrete wall without evidence and then completely destroy the one on the other side of the building. (see footnote)

In my estimation, the average speaker puts out far more bass than anyone would ever know but due to room boundaries and cancellations you only hear a fraction of it. That's why trapping bass at the boundaries of the room makes for less cancelation in the center and almost paradoxically more bass.

(Footnote)

In order to destroy a target or kill or injure enemy personnel using a sonic signal, it is necessary to vibrate the target at or near its resonant frequency. Since the resonant frequency of commonly encountered structural targets is relativelylow, typically 5-20 hertz, a low frequency sonic beam is required. In addition, the sonic beam must have sufficient range to be effective as a weapon. While these two criteria are simple to state, they are not easy to implement. The reason isRayleigh's Law which may be written in equation form as follows:

where

δ equals the radius of the central disc of energy,

λ equals the wavelength of the focused beam and

φ equals the angle subtended by the lens at the focal distance. For example, Rayleigh's Law predicts that the lens diameter required to focus a 10 hertz wave to within a 50 foot diameter zone of focus at a range of one mile is about 26,484feet or about five miles.

Until recently, Rayleigh's Law was thought to be an absolute bar to the long-range propogation of a low frequency wave. Recently, however, it has been recognized that if two colinear sound beams are introduced into a nonlinear transmissionmedium, the interaction between them results in the production of the difference frequency. Thus, if the frequency of one of the beams is f and the frequency of the other beam is 2f, then the difference frequency component will also be f and may be usedto augment the lower frequency sound beam. Moreover, the difference frequency component will have the range characteristics of the higher frequency component. However, this augmentation, commonly referred to as parametric pumping, will only take placeif the phase difference between the two signals at the starting point of the interaction is approximately 90°. Otherwise, the component produced by the non-linear interaction will tend to oppose the lower frequency signal. The theoretical basisfor these conclusions is set forth in an article by O. V. Rudenko and S. I. Soluyan entitled Theoretical Foundations of Nonlinear Acoustics (English translation) Consultant's Bureau, New York 1977, pp. 145-157.

This is great! Thanks for your complete explanation of how bass traps work and how to make them. And with your listening room page http://www.decware.com/myroom/myroom.htm , and the links from that page, you go a long way toward completing the room treatment picture. I have looked a lot at this stuff on the net, and it is not easy with so many opinions and explanations based upon differing means to differing ends. You have faithfully winnowed out the chaff and created usable and understandable concepts and solutions. I appreciate that!

wow!, thank you very much steve, for your information on this subject. You have saved me a ton of headache from screwing up, because i was about to screw up. I am going to buy the book immediately. i was going to build my floor up to a 6" depth, however after reading what you said, i may go deeper. i plan to get the book and read it tomorrow. i am building right now, as we speak...so i need to get to reading.thank you once again for the great information. I really appreciate it.

Dennis, thanks for the reminder. My house is small and my listening room is our main living space with notable theoretical sound problems. I did not see the tried and true direct solutions as realistic tools in this setting, so I walked around it in various ways, not looking for a perfect room, but for one I love the sound of. It has direct absorption put in mainly for bass and low mids and pretty well disguised. The other tools I used have subtle visuals at the forefront, and reasonably good effects. Primary solutions were to carefully tune the speakers and amp to balance out remaining room inadequacies. Not a "perfect room" by any means, but my whole system is one I love with a respectable soundstage and a very convincing and palpable sound. And it still looks a living space for the most part. This is part of what intrigues me about the floor as bass trap concept.

But mine has been a grueling process researching, finding and trying different stuff to finally reach a synergy that suited my tastes. Also I doubt my sound is as good as that of a well designed designating listening room, and it would very likely be more efficient and comfortable to take that already fleshed out route than messing around like I have.

Though I read Steve's articles multiple times through my process, somehow the above entry along with re-reading the articles sort of crystalized the concepts for me.

I will take you up on your suggestion though and order the book. It is a fascinating subject and the book will probably help me figure out more about this room, but there may be a "designed" listening room in my future too. So thanks,

Aloha all, I have been off the site for a few months while I build an addition to my house with a real listening room (yay!) and I just checked in to review Steve's post on the rock wool bubble cloth sequencing. I will be back soon.... mike